The present invention relates to an image information processing method and device for, on main image information, such as a face photograph of a person, recording additional image information, such as security information, in a state of invisibility. Further, the present invention relates to a method of preventing forgery of certificates or the like using the image information processing method.
In recent years, with the promotion of digitization of information and the spread of the Internet, importance has been set on techniques such as digital watermarking, digital signature, and so on. The study of a special encryption scheme, called xe2x80x9cimage deep layer encryptionxe2x80x9d, as one of these techniques has been promoted. This scheme, which records additional information in such a way that it is embedded in main image information in a state of invisibility, provides an effective measure against unauthorized copying, forgery, and tampering of identity cards printed with face photographs and photographs which have copyright information embedded in.
For example, a method of superimposing information on a pseudogradation-represented digital image is disclosed in an article entitled xe2x80x9cEncoding Method of Combining Text Data with an Image of Color Density Patternxe2x80x9d, the Journal of the Institute of Image Electronics, 17-4, 1988, pp. 194-198.
Moreover, Japanese Unexamined Patent Publication No. 4-294862 discloses a method which, on the basis of a hard copy output of a color copying machine, identifies that copying machine.
Furthermore, Japanese Unexamined Patent Publication No. 8-57529 discloses a method of embedding a monochrome bi-level image in a color image using color differences.
However, in the method of combining text data with a color density pattern image with encoding and the method disclosed in the Patent Publication No. 4-294862, image information is only embedded in either an electronic medium or a non-electronic medium (paper). Any technique that can be applied to both the media is not disclosed nor suggested.
The conventional image information processing techniques described above are all intended to deal only with color image information as main image information. That is, no monochrome image information is included in the subject of processing.
Although methods of embedding image information are disclosed, nothing is disclosed for an overall system configuration for embedding, recording, and reproducing image information.
It is an object of the present invention to provide an image information processing method and device which permits composite image information in which additional information is superimposed on main image information to be produced and permits the additional information to be reproduced from the composite image regardless of which of an electronic recording medium and a non-electronic recording medium it has been recorded on.
It is another object of the present invention to provide an image information processing method and a method of preventing the forgery of certificates and so on using the image information processing method which provide great security against forgery without making any difference between color image and black and white image information as recorded images.
In order to achieve the object, according to one aspect of the present invention, there is provided an image processing method comprising the steps of: converting predetermined additional information into a visible additional image to be embedded in a main image; creating a composite image by embedding the additional image in the main image in a state of invisibility; recording the composite image on a recording medium; and extracting the embedded additional image from the composite image recorded on the recording medium to recover the predetermined information.
The conversion step includes a substep of converting the additional information into visible two-valued two-dimensional codes and a substep of modulating the two-dimensional codes using mask pattern information, and the reproduction step includes a substep of extracting the additional image from the composite image using the mask pattern information.
The method of the present invention further comprises a step of converting a full-color main image into an achromatic image composed of R, G, and B components, and the creation step creates the composite image in such a way that it looks black and white to the human visual system and its respective pixel is composed of multiple color components.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.